Method of making molded stems



June 15, 1943. c, A. HORN METHOD OF MAKING MOLDED STEMS Filed April 25,1939 3 Sheets-Sheet 1 lNvENToR. CLARENCE A. HoRN.

'ATTY.

June 15, 1943. c. A HORN 2,321,600

I METHOD OF MAKING MOLDED STEMS Filed April 25, 1939 3 Sheets-Sheet 2BNVENTDR. CLARENCE A. How,

A'TTY.

June 15, 1943. c. A. HORN METHOD OF MAKING MOLDED STEMS 3 Sheets-Sheet 3Filed April 25, 1939 FIG. 10.

FIG.

INVENTOR. CLARENCE A. HORN.

Patented June 15, 1943 METHOD or MAKING MOLDED STEMS Clarence A. Horn,Newton, Mass., assignor to Raytheon Production Corporation, Newton,Mass, a corporation of Delaware Original application February 24, 1939,Serial No.

Divided and this application April 1939, Serial No. 269,871

Claims.

This invention relates to electrical discharge devices comprising sealedenvelopes, such as electron discharge devices and the like, and moreparticularly to a novel stem and a novel method of making such a stem.This application is a division of my co-pendingapplication, Serial No.258,263, filed February 24, 1939.

Attempts have been made to produce. electron discharge tubes with glassenvelopes in which the stem serves as the tube base itself, and whichcarries lead-in conductors which also serve as the external contactpins. Difliculties have been encountered in constructing a stem whichreadily could be sealed to the envelope.

An object of this invention is to devise a stem of the foregoing typewhich can be sealed to an enveloped in a simple, inexpensive andreliable manner.

Another object is to devise such a stem which is inexpensive tomanufacture.

A further objectis to devise a novel method of making such a stem.

The foregoing and other objects of this invention will be bestunderstood from the following description of an e'xempliflcationthereof, reference' being had to the accompanying drawings,

' wherein:

4 Fig. l is aperspective view, partly broken away,

of an electron discharge tube incorporating my novel stem; I

Fig. 2 is a top view of a stem. made in accordance with the presentinvention;

Fig. 3 is a section taken along line 3-3 of Fig. 2;

Fig. 4 is a section taken along line l4 of Fig. 2;

Fig. 5 is a perspective view of the top press block of a machine formolding my novel stem;

Fig. 6 is a perspective view of the bottom press block of such amachine. said figure being placed in juxtaposition to Fig. 5 in order toshow their relative operating positions;

' Figs. 7, 8 and 9 show essential parts of the machine for molding mynovel stem and the successive steps in forming such a stem;

' of the stem 2. These lead-in rods are also rigid so that in thecompleted form of the tube they serve as the external contact pinsadapted to .be inserted into a cooperating tube socket. If desired anumber of dummy support wire 4 may likewise be sealed into the uppersurface of the stem 2. These dummy support wires do not extend throughthe stem, and therefore need not form an air-tight seal therewith. Forthis purpose these dummy support wires may be made of a metal which doesnot make a perfect seal with the glass. They may conveniently be formedof nickel. The usual type of mount 5 is supported by'the lead-in rods 3and the dummy supp r wires 4. The mount 5 may consist of a plurality ofelectrodes, for example, an; anode 6 surrounding a cathode I. In orderto enable the tube to be exhausted, the stem 2 is provided at itscentral portion with an exhaust opening communicating with an exhausttube 8. The bottom of the tube is surrounded by a guard shell lheld inplace on the tubeiby means of a ring or cement It. The guard shell 9 isprovided with a central tubular member I i which surrounds and protectsthe portion of the exhaust tube remaining on the completed tube. Theguard shell 9 is provided with sumciently large openings around each ofv the lead-in rods 3 so that electrical contact be- Figs. 10, 11 and 12show the successive steps I in the sealing of the envelope to the stem;

Fig. 13 is a top view of the mount block used in the apparatus of Figs.10 to 12; and

Fig. 14 is a side view of said mount block. The tube as illustrated inFig. 1 consists of a glass envelope I having a bottom wall consisting ofa stem or base 2. A plurality of lead-in rods 3- are sealed through saidstem 2. These lead-in rods are made of some metal which readily sealstween the shell 8 and the rods '3 is efl'ectively Prevented.

The tube. as illustrated in Fig. 1, is adapted to be inserted in asuitable tube socket, the tubular member I i cooperating with somesuitable locking arrangement, and the pins 3 cooperating with suitablecontact members in' said socket, whereby the proper electricalconnections may be made to the electrode elements within the envelope l.

A tube of the foregoing type presents certain diiliculties andrequirements if such an arrangement is to be commercially successful.Since the lead-in rods-l serve as the external contact members for thetube, they must be kept parallel and maintained accurately in theirpredetermined cir- 4 cular relationship in order that such tubes may fltinterchangeably in standard sockets provided the leadin rods. Anotherrequirement is that the stem 2 may be easily sealed to the envelope I bythe usual type of sealing-in machine. A further requirement is thatduring this sealingin process, the main body of the stem 2 carrying ,thelead-in rods 3 shall not be. subjected to'any distortion which mighttend to upset the requisite positional accuracy of said lead-in rods.Stems made in accordance with my present invention satisfy each of theserequirements, and

produce a tube which satisfies all or the obiects 01' my invention asstated above- My novel stem consists of a. substantially fiat disk ofglass having a central thickened portion 7 also be thick enough tofirmly and definitely support the lead-in rods 3 and thedummy wires '4without cracking. It also must be sufficiently massive so that duringthe sealing of the stem to the envelope I, it is not heated suflicientlyto soften to any appreciable extent. I have found that the thickness ofthis central portion in a particular instance conveniently may bebetween .080 and .095 of an inch. However, thicknesses as low as .060might be feasible in some instances. Surrounding the thickened portioni2 is a thinned edge IS. The top of this edge I3 is preferably disposedin the'same plane as the top of |2, for

, lowingdescription of the mode This upper press mold is provided withholes 23 only for the rods 3, since as previously indicated the dummysupport .wires 4 do not extend through the stem 2. The upper pressmold'likewise is recessed around each opening 23 in order'to provideboss-forming surfaces. The upper press mold is provided with a centralhole 24 for the purpose of receiving the exhaust tube 8, while the lowerpress mold is provided with a central opening 25 through which anexhaust port forming mandrel may project. The upper press block 2| isalso provided with a raised edge 26 surrounding the upper press molddepression 22. This raised edge 20 is of smaller diameter than theraised edge 20, and determines the diameter of the central thickenedportion l2 of the stem. These differences in diameter likewise form thethinned edge l3 as will be evident from the folof manufacture of saidstem.

' Figs. '7, 8 and 9 show the relative operative positions of the upperand lowerpr'ess blocks i6 and 2|. The lower press block I8 is mounted torotate in a fixed plane, while the upper press block is suitably mountedto reciprocate in a vertical line above the lowerpress block. The upperblock 2| is also mounted to rotate in synchronism with said lower pressblock.

The glass for the stem is supplied in the form of two glass rings orcollars 21 and 28, which as shown are set upon the lower press blockIii,

reasons which will be explained below. This thinned edge it must have athickness sufllciently less'than that of the central portion l2, so thatduring the sealing-in process it can soften sumciently to seal readilyto the glass envelope without producing any appreciable softening of thecentral portion I2. I have found that the thickness of the edge l3conveniently may be made about half of the thickness of the centralportion l2. In a particular instance I have used .045 to .055 as athickness of said edge. In the particular examples which I have cited,the thickness of the all of the glass envelope l was between .030 and.050 of an inch. The stem 2 is preferably formed with a lower boss llaround each'lead-in rod 3, and a smaller upper boss I5 around each ofsaid lead-in rods. The bosses ll project through the openings in theguard shell 9, and thus maintain said guard shell. in its properposition as well as insure against electrical contact between said'guard shell and the leadin rods.

In Figs. 5 and 6 I have shown certain essential features of the machinefor molding the novel respectively, inside and outsid of the circle ofholes l8 and I9. The-lead-in rods 3 are then threaded into the openingsl8, and the dummy support wires 4 are threaded into the holes IS. Theinner glass ring is formed, as shown, with the top portion 29 thereofturned in so as to provide a substantial amount of glass alreadypositioned toward the central portion of the stem. This arrangementfacilitates the uniform distribution of glass throughout the extent ofthe stem, and also prevents the melting and sticking of glass onto therods 3 above the maximum desired height. This latter tends to occur whenstraight glass rings of the requisite size are used. The turned-in shapeof the inner glass ring 28 also facilitates the guiding or threading ofthe rods 3 and wires 4 into their respective holes l8 and IS. Theexhaust tube I is also inserted into the opening 24 so-as to be in aposition to be sealed to the stem.

Heat may be conveniently applied to the glass from gas burners Illpositioned to play on the upper rims of the glass rings. As the glasscollars the lead-in rods and wires to form a plastic mass which adheresto the wires,. asshown, for example, in Fig. 8. To sufiiciently softenthe glass 7 and minimize the tendency of said glass to stick around eachof the holes I! and II are recessed in order to provide boss-formingsurfaces. Around-the circular depression i1 is provided a raised edge.20 which forms a'stop beyond which the molten glass during the moldingoperation cannot flow. This edge, therefore,- determines the maximumdiameter of the edge "of the stem. In Fig. 5 is shown the upper pressblock 2| likewise provided with a central circular depression 22 whichforms the upper press mold,

to the lower press mold ll, the lead-in rods! and the adherent mass ofglass are then raised above the lower press mold ll, as shown in Fig. 8.For this purpose a' plunger 3|, provided below the lower press block I8,is raised, pushing the lead-in rods and glass upwardly into the direct Ipath of the gas flames. After the mass of, glass,

has become sufllciently plastic, the upper press block is lowered, andwith the downward movement .of said press block, the molten glass ismolded between the two blocks 2| and II to form therequisiteshapeor-stem as previously described.

. The holes 28 in the upper press block 2| are made of limited depth sothat, during the above molding operation, they come into contact withthe upper ends of the lead-in rods 3. During said molding operation, theplunger 3| is retracted in synchronism with the downward movement of theupper press block 2|. This results in the lead-in rods 3 being pushedthrough the mass of plastic glass. This motion insures an' exactlimitation of the degree to which the glass extends along the lead-inrods 3 to form the bosses 14. The resulting form of said bosses,therefore, is usually slightly recessed around the' rods 3, as shownmore clearly in Fig. 4. Thi particular step insures a remarkableuniformity of the size and position of said bosses l4. During theforegoing molding operation, the exhaust tube 8, the lower end of whichpreviously has been softened by the application of a gas flame thereto,is brought into contact with the central portion of the plastic mass soas to be sealed thereto. To maintain the opening through the exhausttube,

a mandrel 32a is provided which is raised, as Y shown in F g. 9, toconfine the molten glass exteriorly of the inner wall of the exhausttube. The upper press block 21 is then retracted and the completed stemis'permitted-to cool on the lower press block I6. This permits said stemto free-itself from said lower press block, and also insures an accuratealignment of the various elements of the completed stem. The completedstem is then removed from the machine.

After the stem has been completed, the mount is assembled on the lead-inrods 3 and dummy support wires 4. The envelope l is then sealed to thestem around the mount, as illustrated in Figs. to 14, inclusive. Inthese figures there is shown an individual sealing head unit of anenvelope sealing machine. As shown, this unit includes a hollowrotatable member 32 carrying a mount block 33 at its upper end. Thismount block 33 is partly broken away in Fig. 10. The rotatable member 32is provided with a central bore 32" through which air is adapted to beblown. The mount block 33 is likewise provided with a central'bore 34communicating with the bore 32. The mount block 33 is hkewise providedwith a series of holes 35 which are adapted to receive the pins 3 of astem. A series of lugs 36 is Provided on the mount block 33 between eachtwo holes 35. These lugs are spaced sumthe lower portion thereof with anannular shoulder 31. Immediately above said annular shoulder is provideda series of bores 33 which pass from the 'bore 34 to the exterior of themount block. The lower portion of the rotatable member 32 is I providedwith a pair of clutch jaws 40-40 which are normally spring-biasedoutwardly. A tapered sleeve 4| surrounds the rotatable member 32 and isadapted when moved downwardly to force the clamping jaws 40-40 inwardly.

In order to sealthe glass envelope to the stem 2, the stem 2 carryingthe mount 5 is inserted on the sealing-in head by inserting the exhausttube 8 into the bores 34 and 32'. The rods I'ofthe stem 2 are receivedinto the holes 25 and the bottoms of the bosses I4 rest upon the face ofthe block intermediate the lugs 33. Some support also is aflorded by theupper edge of each alternate lug 3i engaging the glass of the steminterithrough the bore 32' and passing through the mediate the bossesl4. The clutch jaws 40- being in their outward position, the exhausttube 8 is free to slide between them so that variation in length, due totemperature expansion, may readily occur. A cylindrical glass envelope42 is then applied over the stem and mount a indicated in Fig. 10. Thisenvelope is conveniently positioned by resting against a pair ofstandards 43 formed as part of the mount 5. Heat is applied byv means ofsuitable gas names 44 adjacent the thinned edge ll of the stem 2. Thisbrings about a softening of the glass at this point,

causing a gradual constriction toward the stem until contact is madewith the thinned edge l3 and fusion of the wall of the envelope 42 andsaid thinned edge l3 occurs. This constriction is aided by the. pressureof the gas flame directed toward the axis of the rotating sleeve in thehead unit. In a subsequent position the gas flames are directed to apoint slightly below the thinned edge l3, the heat produced beingsuflicient to cause a melting of the glass. The weight of the lowerskirt of the glass envelope 42 tends to cause a separation at thethinned edge l3. Inorder to assist this separation, air is blown upthrough the bore 32'. The previous softening of the glass has causedsufllcient constriction thereof so as to contact the annular shoulder31, thus producing a closed pocket between said annular shoulder and thestem 2. The air coming up bores 38 causes an air pressure within thispocket which bursts the plastic glass bubble thus formed and producesthe desired separation at the thinned edge IS. The gas flames arecontinued for a short time around the thinned edge so as to produce auniform rounding of the glass at the point 46.

The sealing-in head then moves out of the region of the gas flames andlair is continued to be blown through the bore -32 for a short period.This air passes up through the bore 34 and out through the spaces leftby the short lugs 36a as well as other intervening spaces between thestem 2 and the mount block 33. This air, which is relatively cool, coolsthe body of the stem 2 so as to insure that said body is solid andrigidduring the subsequent pull-down operation. This prevents any distortionof the main body of the stem and dislocation of the lead-in rods 3during said pull-down.

As shown in Fig. 12, a pair of clamping jaws 45 move inwardly and engagethe envelope 42 while the tapered sleeve 4| is moved downwardly to forcethe clutch jaws 40 into clamping engagement with the exhaust tube 8.Relative motion is then produced between the clutch arms 45 and therotatable member 32 so that the stem 2 is pulled down with respect tothe envelope 42. This pull-down produces the requisite working androunding of the glass at the sealing-in point which is the usual purposeof such a pull-down.

Due, however, to the fact that the main body of the stem 2 is rigid andthe rods 3 are firmly received in the holes 3!, no distortion of saidstem or dislocation of. the rods 3 takes place during such pull-down.The envelope is now ready for exhaustion which takes place through theex-' haust tube 8, after which operation the exhaust tube is sealed ofland the guard shell 3 applied as volving the thickened central portionl2 and thinned edge I3 of the stem 2. I have found that if the internalsurface of the envelope adjacent the sealing-in point 46 (see Fig. 1) iskept tree of all sharp bends and a smooth and rounded contour preserved,substantially all tendency to crack at this point will be eliminated. Byforming the stem 2 with the thinned edge IS in the same plane as theupper surface or said stern,

' this elimination of sharp bend and the preservation of a smoothcontour is readily obtained, since due to the particular constructionwhich I have described, when the edge It is made plastic during thesealing-in process, the wall of the envelope will fuse to this thinnededge I! and form a continuation thereof. During the pull-down operation,the thinned edge l3 will have some slight tendency to be bent upwardly,thus producing a smooth transition curve from the thinned edge l3 to theinterior walls,v of. the envelope. Since the edge i3 is originallyformed as a continuation of the upper surface of the stem 2, this smoothtransition will be carried down withoutbreak or interruption onto theupper surface of said stem 2, as indicated most clearly in Fig. 1. Evenif said edge I! were not formed in this way, the requisite sealing mightstill be accomplished with proper precautions. considerable advantage isstill obtained from the thinned edge l3 irrespective of its relationshipwith respect to either surface of the stem 2.

Of course it is to be understood that this invention is not limited tothe particular details as described above as many equivalents willsuggest themselves to those skilled in the art. Forexample, in someinstances it may be desired to utilize this invention in tubes havingthe conventional' base with additional contacting prongs. Various otherchanges will suggest themselves to those skilled in the art. It isaccordingly desired I that the appended claims be given a broadinterpretation commensurate with the scope of the invention within theart.

What is claimed is:

1. The method of forming a glass seal which comprises forming arelatively thick substantial- .Thus' a,a21,eoo w lyiflat glass wallmember with a relatively thinglass sealing lip projecting from said wallmember, and a plurality of lead-in conductors sealed into said wallmember, heating the side wall of a glass envelope and said sealing lipto sealing plasticity without appreciably plasticizlng said wall member,sealing the outer perimeter only of said sealing lip to the innerplasticized wall of said envelope, cooling said flat wall member whilesaid lip is heated to insure rigidity of said wall member by. blowingcool air thereon, and producing a pull-down between said flat wallmember and said envelope.

3. The method of forming a glass seal which comprises forming arelatively-thick substantially flat glass wall member with a relativelythin glass sealing lip projecting from said wall member, and a pluralityof leadin conductors sealed into said wall member, the top surface ofsaid sealing lip lying in substantially the same plane as the topsurface of said wall member, heating the side wall of a glass envelopeand said sealing lip to sealing plasticity without appreciablyplasticizing said, wall member-,sealing the outer per- 1y flat glasswall member with a relatively thin glass sealing lipprojecting from saidwall member, and a plurality of lead-in conductors sealed into said wallmember, heating the side wall of a glass envelope and said sealing lipto sealing plasticity without appreciably plasticizing said wall member,sealing the outer perimeter only of said sealing lip to the innerplasticlzed wall of said envelope, cooling said flat wall member whilesaid lip is heated to insure rigidity of said wall member, and producinga pull-down between said fiat wall member and said envelope.

2. The method of forming a glass seal which comprises forming arelatively thick substantialimeter only of said sealingedge to the innerplasticized wall of said envelope, cooling said flat wall member whilesaid lip is heated to insure rigidity of said wall member, and producinga pull-down between said flat wall member and said envelope.-

4. The method of forming a glass seal which comprises forming a stemwith a plurality of lead-in conductors sealed into a wall member,

and a glass sealingedge projecting from said wall member, placingan-open-ended glass. envelope over said stem, sealing said sealing edgeto the inner wall 01. saidenvelope, bringing the lower side wall of saidenvelope below said stem into engagement with an annular shoulder toform a pocket between said stem and said shoulder, softening theenvelope wall'belowsaid stem, and blowing air into said pocket to'severthe glass 0! said envelope below said stem from the rest of thestructure.-

5. The method oi. forming a glass seal which comprises'rorming arelatively thick substantially flat glass wall member with a relativelythin glass sealing edge projecting from said wall member, and aplurality oi! lead-in conductors sealed into said wall member, placingan openended glass envelope over said wall member, sealing said sealingedge to the inner wall of said envelope, bringing the lower side wall ofsaid enenvelope wall below said stem, and blowing air into said pocketto sever the glass of said envelope below said stem from the rest of thestruc- CLARENCE A. HORN.

